Transistorized television camera



Feb. 12, 1963 L; ROY G.sc;H1 lc|-|T 3,077,517

TRANSISTORIZED TELEvsIoN CAMERA 5 sheets-sheet 1 Filed Aug. 5. 1960 5 Sheets-Sheet 2 LE ROY G. SCHLICHT TRANSISTORIZED TELEVISION CAMERA Feb. 12, 1963 Filed Aug. 5. 1960 Feb. 12, 1963 LE ROY G. scHLlcHT 3,077,517

TRANsIsToRIzED TELEVISION CAMERA Filed Aug. 5, 1960 5 sheets-sheet :s

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Feb. l2, 1963 LE RoY G. scHLlc'H-r 3,077,517

TRANSISTORIZ'ED TELEVISION CAMERA 5 Sheets-Sheet 4 Filed Aug. 5, 1960 Ima MNN

Feb. l2, 1963 LE ROY G. scHLlcH-r 3,077,517

y"rRANsIsToRIzED TELEVISION CAMERA Filed Aug. 5, 1960 5 Sheets-Sheet 5 figg w United States 3,077,517 TRANSISTGRIZED TELEVISIONCAMERA Le vRoy. G. Schlicht, Anaheim, Calif., assigner to Packard- ,Bell .Electronics Corporation, Los Angeles, Calif., a lcorporaton'of California Filed Aug.f5,'1960, Ser. No. 47,735 14 Claims. (Cl. '178-712) vThis'inventi'o'n' relates to television systems and, more particularly, to an economical, compact yand efficient television camera for VVuse essentially "in closed television systems. Y

`rlTelevision `systems a're'unique iii-electrical communicafti'o'n in that they extend the y.rangeofv 'isit'infof' an vobserver. This Acharacteristic leads to a wide range clap- Iplicatio'ns in telemetering and 'monitoring 4'of `operations which take place "in remote locations. 'Forie'x'arnple a single guard may simultaneously rmonitor or watch a number-of remotepositions. 'Such systems are generally Areferred to as' closed systems-because the lcameras arecon- Ynectedxto the viewing equipment "by cble'orwiefacilities.

Closed, systems'have utility in rnalny "applications 'but .the extended use of the systems have 'been"1imited"' b`y theircost The major cost of the television'syster'n is "the cost of the camera which is generally manytinsmore expensivethan the monitor orreceiver. In aspeciiic ilIustrative embodiment of this invention, a relativelyinexpensivebut high quality television camera visprovidedutiliz- ,ing transistor circuitry. When transistor circuitry is employed, the usual-advantages of transistors are achieved .with regard to size and power requirements, but the -utilization of transistors'introduces a number of problems. For example, due to the relatively low interelectr'ode transistor impedances, transistor circuitry'even of the emit- .ter-follow type generally utilized for isolation, is inefcient for receiving television signals from a Vidicon 'or other picture tube.

In the specific illustrative embodiment of this invention, a double feedback loop i-s utilized in conjunction with a transistor emitter follower to provide a high impedance at the output of the Vidicon tube. A very high impedance load impedance is utilized for the Vidicon tube so that a long time constant is provided lforvchan'ging the signal level. In prior systems, 1a complicated arrangement including sampling means, rectitiers and lters are used to slow down the signal level variationfso that different light level scenes may be viewed in 'succession without delay. The utilization of a single load resistor for this function effects a considerable economy.

Other features of this invention relate to the provision of means for maintaining the linearity of the vertical sweep signals with variations in magnitude so that a linearity control is unnecessary.V The horizontal and kvertical sweep signals are provided respectively` to two control transistors connected in parallel which perform a'number of functions: The control transistors function as protective means because in the event of a sweepl failure, eitherhorizontal or vertical, the transistors blank the Vidicon`beam to protect the Vidicon; the control transistors provide Yfor retrace blanking; and the control transistors are part of circuit means for producing synchronization Vsignals .for transmission to a monitor or receiver for viewingthe television signals. c,

Further features of this invention pertainfto ,the utilization of a combination of vacuum tube'and transistor circuitry to effect the advantages of each. vFor example, the oscillator or multivibrator for generating the horizontal frequency lsignals is a vacuum tubecircuitand is designed to have a warmup time comparable to or'large'r than that of the Vidicon tube. During warmup of the lhorizontal multivibrator, the control transistors blank the Vidicon tube. -oofoperates yvi/ith`the control transistors to'protect the Vidiconl tube. v4'amplifier Ais utilized'"at "the output end of the vtransistor vvideo"amplifierchain. 'Th'evideo signals vmay be taken Adirectlyfrom thevideo chain lto 'a monitor, and the impedance isolation'is desirabletoprevent transistor burnout duel to'diie'rences i Yand the camera.

3,077,517 Patented, .Feb 12, lass Thehorizontal multivibrator, accordingly,

:As another illustration, a vacuum tube in potentialbetween the monitor vurther advantages 4andfeatures`of thisinvention will beco'rne apparent upon consideration o f'the'follo'wing description when re`"d"in conjunction with the drawing wherein:

FIGURE l is`a perspective 'view ofthetelevision camera of this invention;

`FIGURE '2 is a'pers'pec'tive view of `va' remote control ilunit associated with the televisin camera;

-FIGURES is 'a circuit-representation of the-video amplifier chassis of thetelevisioncamera of'this invention;

FIGURE "4 is a circuit representation of `the deflection `chassis of vthe television cameraoff'this invention;

FIGURE 5 is Aa circuit representation of the camera controluni-t"associated ywith the television camera of this invention; and

FIGURE '6 is a series of curves illustrating the operation of the'deliection chassis of this invention. t

amera 10 is Referringiirst to FIGURE l, a television `c ydepicted'having 'alens 11 which maybe, illustratively, a 125 mm-/ 1.9 'lens for viewing `an area to be televised.

Thecam'e'ra 10 does not include vany control knobs as the control'fu'nctions are provided by a camera control unit 15 depicted in'FIGURE 2. The television camera l10 is coupled by a cable 12 to a cable 19 extending from the control unit 15. Thefcontrol unit 15y includes three control knobsl, 17 and 18. The control knob 1 6 functions as V an on-oi control for the unit 15 and for the camera 10, and also to adjust the brightness of the television imageprovided by the camera 10. The'knob 17 is utilized to'focus the television'image, and the control knob 18 is-utilized to adjust the contrast vof the video image provided by the camera 10.

When the knob `16 'is rotated, i-t closes a'vswitch 31,

'shown in the circuit representation of the control unit 15 .in FIGURE 5, to introduce power from the leads 30 to a transformer 32. One of the input leads 30 is coupled through a fuse 34, which may have a rating of `2 amperes, to the transformer 32. The alternatingcurrent signal across the secondary 35 of thetransforrner 32l is rectified by four diode-s 36-39 coupled serially in pairs to provide for* sufficient vpeak inverse voltage rating. The diodes 3 6-39 'are coupled to a lilter arangement including two capacitors 46 and 48 and a resistor 47. The capacitors 46 and 48 may have'suitable values such as 40 microfarads andthe resistor 47 va suitable value such as 5 kilohrns. The iiltered signalis provided across a potentiometer '50 which lis controlled by the tknob 17 v at the front of the camera control unit-15 in FIGURE 2. The potential from the adjustable tap of the potentiometer 50 is provided through a lead 19a of a cable toa resistor 220 in FIGURE 3 vat the output yof the Vidicon tube 2.5. The voltage provided from the potentiometer -505 may be from 0 to I-280 volts. AThe circuits'shown in FIGURES 3 and \4 represent portions of the -television camera 10 shown in FIGURE l.

A negative supply voltage of 280 volts is-produced by the serially'connected diodes :4l-rand 4 9 which are coupled to one terminal of the secondary lwinding 35. The negative voltage through *the diodes 43 and y49 :is introduced across 'a lte'r capacitor 53 shoutedA by a resistor 52. The capacitor 53 may have a'value of 4D rni'c'rofarads and the resistor 52 mayliave a value of 12 0/kilohms. The filtered negative potential is provided through a yresistor 54 to only 108 milliseconds, only 20 percentof'the saw tooth wave is developed across the capacitors 139 and 145. The capacitors 139 and 145 function as integrating means for developing the saw tooth wave depicted in curve 6e.

Since only a relatively small portion of the saw tooth wave i is utilized, the linearity thereof is good.

The transistor 132 drives a transistor 148 through a coupling capacitor 140 which may have a value of 200 microfarads. The load driven by the Vtransistor 132 is relatively small due to a positive feedback connection from the emitter electrode of the transistor 148 through a resistor 144, which may have a value of 150 ohms, to the junction of the capacitors 139 and 145. The positive feedback conection eifectively decreases the impedance seen by the transistor 132 and, therefore, the time constant of the integrating arrangement to provide for improved linearity of the developed saw tooth wave.

The vertical size of the video image is controlled by a rheostat 154 which is coupled to the emitter electrode of the transistor 1148. The rheostat 154 controls the current through the transistor 148 and, at the Sametime, the amount of feedback. The amount of feedback is reduced or increased in direction and by an amount dependent upon changes in the current through the transistor 148, thus maintaining the linearity throughout theentire range of control and eliminating the need of a separate linearity control. ln prior arrangements,adjustments of the height of the video image varied the time constant so that a linearity control was required.

The current saw tooth signal at the collector electrode of the transistor 148 is developed across acollector resistor 149 and directly coupled to a vertical deflection coil or yoke 152 of the `Vidicon tube 25 in FIGURE 3. The saw tooth deflection signal is 'shown as curve F in FIGURE 6. The coil 152 is shown in FlGURE 4 as part of the circuit 350 merely as a convenience'to avoid the showing of lengthy leads from the collector electrode of the transistor 148 to the tube 25. The path through the coil 152 is returned through a capacitor 150 which may have a value of 200 microfarads to` eliminate the flow of direct current in the deflection coil which would develop a magnetic field and olset the Vidicon beam.

The vertical deflection signal at the collector electrode of the transistor 148 is'also capacitively coupled through a capacitor 163 having a value of 0.68 microfarad to the base electrode of a transistor 169. The transistor 169 is one of two paralleled transistors 169 and 17u, which funtions, as is hereinafter described, Vas a protecting and blanking arrangement for the Vidicon tube 25.

As indicated above, the horizontal deflection pulses are produced in the camera control unit 15 shown in FlG- URE 5. The horizontal drive pulses are developed by the vacuum tube 60 which is connected in a multivibrator arrangement. The warm-up time of the vacuum tube 60 is approximately the same as the warm-up time of the Vidicon tube 25. The tube 60, accordingly, provides for a time delay to blank the electron beam in the Vidicon tube 25 until the horizontal deflection signals are being produced. The horizontal deflection signal, as is hereinafter described, is introduced to the protect and blanking circuit including the two paralleled transistors 169 and 170 brieiiy mentioned above.

The multivibrator, including the tube 60, is a conventional cathode coupled free running multivibrator having a frequency controlled by the time constant of a stabilization coil 80 and a capacitor 78 shunting the coil 80. The parallel arrangement of the inductor 80 and the capacitor 70 is coupled to an anoderesistor 75 which may have a value of 5.8 ltilohms. The capacitor 7S may have a value of 0.004 microfarad. Anode potential is provided from the filter consisting of the `capacitors 46 and 4S and the resistor 47, described above. The grid of the left triode section of the tube 60 is coupled by a grid resistor 82 shunted by a capacitor 31 to the common ground junction, and the grid of the right triode section of the tube tion. The capacitor 81 may have a value of 0.003 microfarad and the resistors 82 and 86 may have respective values of 470 kilohms and1100 kilohms each. A common cathode resistor 83 is provided which may have a value of 2.2 kilohms. The anode of the left triode section is capacitively coupled to the grid of the right triode section by a capacitor 77 which may have a value of 1 microfarad. Anode potential4 is provided to Y.the right triode section of the tube 60 by a resistor 79 which may have a value of kilohms. Y

The pulses from the free running multivibrator including the tube 6i)A are coupled through a capacitor 8S to a step down transformerk87 andther'efromrto av coaxial cable 19] which forms part of the cable 19 to thev deflection circuit 350 in FIGURE 4. The capacitorSS may have a value of 0.1 microfarad. At the circuit 350, the coaxial cable 19] terminates ina load resistor-184-which may have a value of 68 ohms. The pulsesacross the resistor 184 are shown 'in curve G of FIGURE andare provided ata repetition rate of 15,750 pulses permsecond which is the horizontal' line frequenc :y yof conventional video signals. The'time base of the diifere'nt curves in FIGURE 6 are different because thever'tical deection pulses 'at a frequency of 60 cycles per second whereas the horizontal pulses are at a frequency of 15,750 cycles fper second. The pulses across theresistor184 are coupled v"through ay capacitor 185 to 'a' class B type amplier in- Vadjustable -inductor 178j`coupledto its collector electrode and a resistor 174 coupled t-o its base electrode. Positive overshoot is clipped by a `diode 187, shuntedby a iresistor 4186, coupled between the base electrode 'and lt-he common ground junction. The resistors 186 and 174 vmay have lvalues of '820 ohms and 2.2 kilohms respectively, the capacitor 1185 may have a Value of 0.22 microfarads and the rheostat 1713 may have -a maximum resistance of 100 ohms. Y l

The transistor 188 isdriven to saturation to develop negative pulses at the collector electrode ofthe transistor 188 which are 'idepietedin curve H of FIGURE '6 and which have an amplitude of approximately 60l volts. The inductor 178 in the collector circuit of the 'transistor 183 functions to develop the relatively` large .amplitude neg-a- -t-ive pulses. The negative, horizontal pulses are coupled through a capacitor 180 and a transformer 190 tothe horizontal deflectioncoils 191 of the Vidicon tube 2,5. v

The transformer 190 provides `D.C. isolation and imped- `anos matching between the coils 191 and the classB arnplier including the transistor .188. The horizontal deflection coils 191 are connected in parallel to reduce the inductance of the windings by fou-r times thus reducing the ldriving voltage requirements, .and'to facilitate the utilization of transistor circuitry. Y

IIn the event of a sweep lfailure of the Vid-icon tube 25, it is desirable to turn oif the yelectron beam in the tube 25 to prevent burning of the target 25a by'repetitive sweeps lfalling on the same rplace onthe targetZSa for more than a few milliseconds. 'Ihe transistors 169 'and 170 Adescribed above, which form al protecting gandblanking circ-uit arrangement, are utilized to turn olfV the 'Vidicon beam in the event ofa sweep failure as well as to provide for the blanking of .the beam between horizontal sweep signals. The transistors 169 and 170 have both emitter electrodes and Vcollector electrodes coupled together. A positivepotential of 45 volts regulated'by a Zener diode 167 is provided to the emitterelectrodes of the transistorsg1o9 and 170. The Zener diode 167 may be a silicon diode 1N625 which functions Vto clip oft positive pulses to protect the'tr'ansistors f'rom'excessive biasing potential. The diode ,167 Valso vshunts 'the base-to-collector paths .of the transistor y169 yto 4compensate for leakage resistance.

Each of the transistors 169 and 17h is biased so that the absence of an input signal at its base electrode will cause saturating current flow. rihe emitter-to-base junction of the transistor i469` is forward biased because its base electrode is connected to ground by the resistor 165 Whereas its emitter electrode is at +45 volts. Similarly, the emitter-to-base junction of the transistor 17o is forward-biased because its base electrode is connected to ground by the resistor 17o. The resistor 165 may have a value of l megohrnand the resistor 197 may have a value of 68 kilohms.

When either of the transistors is saturated, the full emitter potential appears across the serially connected collector resistors 214 and 21S and is applied to the cathode of the tube 25 through a lead X. The resistors 214 and V215 serve as the cathode resistors for the Vidieon tube 25 so that if neither sweep voltage is present, the cathode of the tube 25 is driven to +45 volts (the emitter potential) to cut ofi the Vidicon beam. The; vertical and horizontal sweep potentials are applied res; ec-

Ytively to the base electrodes of the transistors 16S and 17) with the respective transistors being driven to saturation during the sweep retrace tirne. rlIhe ver-tical sweep potential is provided from the transistor 1445s through the coupling capacitor 163 to the base electrode of the transistor 169.

The horizontal sweep signals are provided from the transformer 19@ through a diode 193 shunted by a capacitor 192 having a value of 0.095 microfarads. The negative pulses through the diode 193 are provided across a capacitor 195 and through a capacitor 194ito the base resistor 197. The capacitors 194 and 195 may have values of 0.05 microfarads and 0.005 microfarads respectively. If either one of the two transistors 169` and 17u is, accordingly, conductive due to a negative potential at its base electrode, current llows through its emitter-to-collector path and the collector resistors 214 and 21S to the common junction or ground connection. Collector bias is provided to the two transistors 16h and 170 from lead 19K through the cable 19, resistors 21h and 162 and a neon tube 161. The resistors 218 and 162 are serially connected with a resistor 16h to the ground junction. The resistors 218, 162 and 166 may have respective values of 47 kilohms, 1.2 megohms and 560 kilohms. The average collector voltage changes from approximately +45 volts to approximately 12.5 volts when either of the transistors 169 and 176 becomes conductive. The neon lamp 161 acts as a sweep indicator because it is energized as long as sweeps are present. Should a sweep failure occur, the lamp 161 eXtinguishes.

The positive potential developed across the resistor 215 is coupled through a capacitor 212 to an inverter arrangement including a transistor 21?. The arnplier is driven to saturation to provide clean clipped pulses which are coupled to the output video line through an emitter follower including a transistor Zhi?. These pulses, shown as curve I in FIGURE 6, serve as the composite synchronizing pulses for the television receiver or monitor, notshown. The emitter electrode of the transistor 21@ is coupled to an emitter resistor 213 having a vaine of 150 ohms. The transistor is self-biased -by a resistor 2tlg collected between its base and collector electrodes and also having a value of 150 ohms. Collector bias is provided through a resistor 206 which may have a value of 2.2 kilohms. The inverted positive pulses are coupled through a capacitor 204 having a value of microfarads to the base electrode of the transistor Zilli. The transistor 200 is self-biased by a resistor 261 having a value of 150 kilohms and coupled between its base and collector electrodes. The transistor zii@ does not invert the vpulses coupled thereto, providing its output from its emitter to a resistor 202 which is selected to provide a potential of 0.5 to l volt peak-to-peak at the output cable of the 5 volt camera lil. The pulses are shown in curve spective horizontal and vertical ilyback intervals.

.l of FIGURE 6. As is hereinafter described, these synchronizing pulses are added to the video signal after it has been amplified by the circuit 2'@ shown in 3.

As indicated above, if either or" the transistors 169 and 17@ is conductive, the beam in the pick-up tube 25 is blanked. These transistors are saturated during the re- The potential at the multipled collector electrode is provided through a lead X to the cathode of the pics-up tube 25. he beam is accordingly blanke-d during the vertical and horizontal flyback intervals. The blanlring pulses at the collector electrodes are depicted in curve l of FGURE 6.

The target 25a of the Vidicon pick-up tube Z5 provides a very high impedance output to the video amplifier circuit Ztl illustrated in F GUlE 3. To present the necessary high impedance input a transistor coupled to the target 25ct of the tube 25 is connected in an emitter' follower arrangement. The target 25a is coupled through a capacitor 223, which may have a value of @.Gl microfarads, to the base electrode of the transistor 239. rthe transistor 23d, as Well as 6 other transistors 21th, 25d, 275, 291, Elli?.` and 321, which are included in the video amplifier circuit Ztl may be PNP junction type transistors 2Nl396. The collector electrode of the transistor 239 is biased from the l5 volt lead through resistors 3555', 243 and 225 which effectively form a voltage divider arrangement. The values of the resistors 3h52', 243 and 22S may be respectively 220 ohms, 180 ohrns and l kilohm. The junction of the resistors 263 and 22.8 is coupled to the common ground connection by a capacitor 226, the junction of the resistors Stt and 263 is coupled to the ground connection by a capacitor and the other terminal of the resistor 3%'5 is coupled to the ground connection by a capacitor 322. The capacitors 322, 2-@7 and 226 may all be 500 cicrofarad capacitors. The potentials provided by this arrangement to the transistor circuitry is, accordingly, substantially direct current.

ln addition to the utilization of the transistor 236 in an emitter follower arrangement, to further raise the amplifier input impedance, negative feedback is applied to the junction of two base bias resistors 233 and 235 which may have values respectively or" l2 lc'lohms and 2.2 kilohms. The base electrode of the transistor 233 is biased by a serial circuit arrangement including a resistor 224i and the two resistors 23:3 and 234. The resistor 224 may have a suitable value such as 82 kilohms so tha-t the emitter-to-base junction of the transistor 23@ is forward biased by a relatively small potential. lhe output from the emitter follower including the transistor 239 is taken from across an emitter resistor 253 connected between the common connection or junction and the emitter electrode of the transistor 239. The output is coupled directly to the base electrode of a transistor 214i? which provides the necessary phase inversion for the negative feedback to the junction of the base resistors 233 and 235. The feedback is provided rorn the emitter electrode of the transistor 2li@ through a coupling capacitor 25S which may have a value of 40 microfarads. rfhe emitter electrode of the transistor Zeil is coupled by an emitter resistor 257 to the common junction and its collector electrode ir" biased by a path through an inductor 241, a resistor 242 and the resistors 243 and The inductor 241, which may have a value of l2 microhenries, functions to increase the response of the amplifier at the higher frequencies. The resistor may have a value of l kilohm.

The negative feedback from the emitter of the transistor 2A@ serves a two-fold purpose by raising the input impedance of the second stage including the transistor' 24@ as well as in the input impedance of the first stage including the transistor 23d. This large negative feedback also functions to improve the transient and frequency response of both stages.

A capacitor 231, illustratively of 40 microfarads, is

shown in phantom coupled between the'collector electrode of the transistor 230 and the emitter electrode of the transistor 24d. The capacitor 241i serves as a bypass capacitor to couple the signal at the collector of the transistor 230 directly to the feedback path. The effect is cumulative to increase the feedback and accordingly the impedance presented by the two transistor'stages. The cumulative effect lof enhancing the impedance provides for-good frequency response while'permitting substantial variation of transistor characteristics. In addition to this transistor arrangement, as described above, the very large load resistor 222, mentioned above, is

`utilized at the 'output of the Vidicon pick up tube 25.

The video signal, illustrated in curve A of FIGURE 6,

at the collector electrode of the transistor 244i is coupled to four substantially identical cascaded 'amplifier stages includingthe transistors 254, 275, 291 and 362, respectively. The stages are conventional video ampliers having shunt peaking provided by an inductor which may have a value of l2 microhenries. The inductor 252 at the collector electrode of the transistor 254 is serially connected wi-th a resistor 250 to the collector electrode of the transistor 254. The base electrode of the transistor 254 is biased by a circuit arrangement including two resistors 277 and 269. The resistors 277 and 2,69 may have values such as l()l kilohms and 330 ohms. The emitter electrode of the transistor 254 is connected to the common junction by an emitter resistor 270 shuntedI by a capacitor 271. The emitter resistor may have la value of 180 ohms and the capacitor may have a value of 150 microfarads. The emitter bypass capacitor 271 shapes Athe response of the amplifier stage by providing low frequency degeneration.

The output from the amplifier stage is provided from the collector electrode of the transistor 254 through a coupling capacitor 256 to the base electrode of the transistor 27S in the next stage. The capacitor 255 may have a value of 40 microarads. The base electrode of the transistor 175 is biased over a path through the resistors 242 and 273 which may have values respectively of 23 kilohms and 2.2 kilohms. The succeeding stages, including respectively the transistors 275, 291 and 362, are identical except for the value of the bypass emitter capacitor. The bypass emit-ter capacitor `2% coupled to the emitter electrode of the transistor 275 is variable so that the frequency response may be increased or decreased. A capacitor Still coupled to the emitter electrode of the transistor 291 may have a value of 0.6010 microarad, and a capacitor 316 coupled to the emitter electrode of the transistor 3112 may have a value ot 150 microfarads.

Because transistor parameters may vary considerably and component tolerances may tend to be additive, the resistor 269, mentioned above, is selected for the amplifier chassis 20 to control the overall gain thereof. The resistor 269 may be a rheostat to facilitate the adjustment.

To supply the current necessary to drive a 72 ohm coaxial line, the ampliiier stage including the transistor 3%2 is coupled to the coaxial line by an emitter follower stage including the transistor 321. The collector electrode of the transistor 3ii2 is coupled by a capacitor 312 having a value of 40 microfarads to the base electrode of the transistor 321. The base electrode is biased over a path including two resistors 310 and 313 which may have values of 2.2 ltilohms each. The collector electrode is directly coupled to the -15 Volt lead and its emitter electrode is connected to the common junction by an emitter resistor 323 which may have a value of 820 ohms. The output from the emitter follower stage, illustrated by curve B in FGURE 6, is coupled through a capacitor 325, which may have a value of 250 micro- .farads, through the coaxial line 19d to the control unit 15. At the unit 15, the video signal is introduced through l microfarad, is connected to Vvideo signals to either of the output terminals vides for an additional drive for the video output signals.

It serves to isolate the transistor circuitry from the video receiver or monitor, not shown, at which the signals are provided.

The capacitor 107, which may have a value of 0.1 the grid of the left triode section of the double triode 64. A grid leak .resistor 108 is coupled from the grid to the ground connection and the cathode of the triode is coupled by a cathode resistor 1119 to the ground connection. The resistors 1%8 and 169 may have values of 470 kilohms and 4.7 kilohms. A resistor 112 is serially connected with the resistor 109 and may have a value of 1.8 kilohms. The cathodes and anodes of the two triode'sections of the tube 64 are also fconnected in common so that the effective arrangement is that koia single large triode. The video output is taken from the cathodes and provided to an output'terminal 114. The .anodes are biased over a path through a resistor 110, which may `have a value of 2.5 kilohrns,

4television monitor, not shown, receives the television signals. When a conventional television receiver is to be utilized for receiving the television signals, the .television signals vmust be suitably modulated on a carrier. The tube 62 is a pentode tube which develops the carrier signal and which modulates thetelevision signals on the carrier. The cathode and control grid and screen grid of `the pentode 62 form part of the oscillator and the anode, suppressorgrid and screen grid form part of the modulator. The frequency of the carrier is determined by a tuned arrangement 97 which includes a capacitor 9S and a capacitor 99 shunted by an inductor 1%. The capacitors 9S and 97 may have values of 22 micromicroarads and 5.25 microfarads respectively, and the arrangement is coupled between the control and screen `grids of the tube 62. Potential is provided to the tuned arrangement 97 from the junction of two anode resistors "91 and 92 through a resistor 93 and a resistor 1111 to a tap on the inductor 161i. The tap is capacitively coupled to ground by a capacitor 1112. The resistors 91, 92,

y93 and 191 may have values respectively of 82 kilohms,

1 kilohm, 47 kilohms and l0 ohms. The capacitor 1li-2 and two capacitors 9d and 95 which respectively shunt the resistors 91 and 93 to ground may have values respectively of 0.001 microfarad, 40 microfarads and 40 microfarads.

The video signals through the coaxial cable 19d from the circuit 2@ are introduced through a capacitor 10S to the suppressor grid of the tube 62. The opposite terminals of the capacitor 105, which may have a value of '0.47 microfarads, are coupled to ground through resistors 1de and 103. These resistors may have values respectively of 75 ohms and 15 kilohms. The modulated carrier is provided from the anode of the tube 62 through 'a capacitor 96 having a value of 0.001 microfarads to an output terminal 113. 1n the event a conventional television receiver is utilized for providing the video ima se, the output terminal 113 is, accordingly, utilized. The 114 and 113 include the signals developed by thepick-up tube 25 as amplified by the transistor stages of the circuit 2i) and also the synchronizing pulses as developed by the transistor circuitry of the deiiection circuit 351i in FGURE 4. As described above and illustrated in FIGURE 3, the synchronizing pulses from the deiiection circuit 3519 are multipled to the coaxial cable 19d with the video signals through the transistor amplifier circuit 20. l

Although this invention has been disclosed and -illustions which will be apparent to persons skilled in the art.

The invention is, therefore, to be limited only as indicated y by the scope of the appended claims.

I claim:

l. in a television camera, a pick-up tube for developing video signals, said pick-up tube having means for developing a beam of electrons and a light sensitive surface for receiving the beam, a DC. biasing arrangement coupled to said lightV sensitive surface and including a resistance over 100 megohms for limiting the rate of change of DC. current from said surface, a video ampliier, and means for capacitively coupling said amplifier' to said surface, said video ampliiier including a transistor' emitter-follower stage connected by said coupling means to said surface, a transistor amplifier stage coupled to the output of said emitter-follow stage, and a negative feedback loop coupled from the output of said amplier stage to the input of said emitter-follower stage whereby the effective impedance presented by both stages is increased.

2. ln a television camera, a pick-up tube for developing video signals, said pick-up tube having means for developing a beam of electrons and a light sensitive surface for receiving the beam, a video ampliiier, and means for capacitively coupling said amplilier to said surface, said video amplifier including a transistor emitter-follower stage connected by said coupling means to said surface, a transistor ampliiier stage coupled to the output of said emitter-follow stage, and a negative feedback loop coupled from the output of said amplier stage to the input of said emitter-follower stage whereby the eliective impedance presented by both stages is increased.

i3. In a television camera, a pick-up tube for developing video signals, said pick-up tube having means for developing a beam of electrons and a light sensitive surface for receiving the beam, means coupled to said tube for generating vertical and horizontal sweep signals and for introducing the generated signals to said tube for controlling the motion of the beam in said tube, and protection circuit means coupled to both said tube and said generating means for monitoring the generated signals and for blanlring said tube when either the vertical or horizontal sweep signals are absent.

4. in a television camera in accordance with claim 3 wherein said protection circuit includes a iirst and a second transistor each having base, emitter and collector electrodes, means directly connecting said emitter elec- .trodes to each other and said collector electrodes to each other, biasing means connected to the base, em ter and collector electrodes of both of said rst and said second transistors for normally causing said iirst 4and said second transistors to be saturated, means connected to said generating means for introducing the horizontal sweep signal to the base electrode of said rst transistor for inhibiting conduction in said iirst transistor and the vertical sweep signal to the base electrode of said second transistor for inhibiting conduction in said second transistor, and means coupled to said tube for introducing the potential of the collector electrodes of said lirst and Said second transistors to said tube whereby said tube is blanked if either the vertical or horizontal sweep signals are absent.

5. in a television camera in accordance with claim 3 wherein said protection circuit includes means coupled to said tube for normally blanking said tube and means coupled to said blanking means and responsive to both the vertical and the horizontal sweep signals for operating said blauking means to unblank said tube.

6. In a television camera, a pick-up tube for developing video signals, said pick-up tube having means for developing a beam of electrons and a light sensitive surface for receiving the beam, a video amplifier, and means for capacitively coupling said ampliner to said surface, means coupled to said tube for generating vertical and horizontal sweep signals and for introducing the generated signals to said tube for controlling the motion of the beam in said tube, and protection circuit means coupled to both said tube and said generating means for monitoring the generated signals and for blanking said tube if either the vertical or horizontal sweep signals are absent, said protection circuit means including means for blanlring said tube during the ilyback portions of both the vertical and horizontal sweep signals from said genrating means, and a synchronizing pulse ampliiier coupled to said blanlcing means of said protection circuit means and to the output of said video amplifier for developing a synchronizing pulse each time said blanking means blanks the beam of said tube for addition to the amplified signals from said video amplifier.

7. ln a television camera in accordance with claim 6 wherein said video ampliiier includes a transistor emitterfollower stage connected by said coupling means to said surface, a transistor amplier stage coupled to the output of said emitter-follow stage, and a negative feedback loop coupled from the output of said amplier stage to the input of said emitter-follower stage whereby the edective impedance presented by both stages is increased.

8. ln a television camera, a pick-up tube for developing video signals, said pick-up tube having means for developing a beam ot electrons and a light sensitive surface ior receiving the beam, means coupled to said tube for generating vertical and horizontal sweep signals and for introducing the generated signals to said tube for controlling the motion of the beam in said tube, said generating means including a source of alternating current, a saturating transistor amplifier coupled to said source for amplifying the alternating current, an integrating circuit coupled to said transistor amplilier and having a relatively long time constant compared to a cycle of the alternating current from said source, an adjustable transistor amplifier coupled to the output of said integrating circuit and to said tube for controlling the size of the image scanned by said tube, and a positive feedback circuit coupled from the output of said adjustable amplifier to the integrating circuit for maintaining the linearity of the signal developed by the integrating circuit with adjustments of the size of the image scanned by said tube at said adjustable amplier.

9. In a television camera, a pick-up tube for developing video signals, said pick-up tube having means for developing a beam ot electrons and a light sensitive surface for receiving the beam, means coupled to said tube for generating vertical and horizontal sweep signals and for introducing the generated signals to said tube for controlling the motion of the beam in said tube, said generating means including a source of alternating current, a saturating transistor ampliier coupled to said source for amplifying the alternating current, an integrating circuit coupled to said transistor amplilier and having a relatively long time constant compared to a cycle of the alternating current from said source, an adjustable transistor amplier coupled to the output of said integrating circuit and to said tube for controlling the size of the image scanned by said tube, and a positive feedback circuit coupled from the output of said adjustable amplifier to the integrating circuit for maintaining the linearity of the signal developed by the integrating circuit with adjustments ot the size or" the image scanned by said tube at said adjustable amplifier, and a protection circuit coupled to both said tube and said generating means for monitoring the generated signals and for blanking said tube if either the vertical or horizontal sweep signals are absent.

l0. In a television camera in accordance with claim 9 wherein said protection circuit includes a rst and second transistor each having base, emitter and collector electrodes, means directly connecting said emitter electrodes to each other and said collector electrodes to each other, biasing means connected to the base, emitter and collector electrodes of both of said first and said second transistors for normally causing said first and said second transistors to be saturated, means connected to said generating means for introducing the horizontal sweep signal to the base electrode of said first transistor for inhibiting conduction in said first transistor and the vertical sweep signal to the base electrode of said second transistor for inhibiting conduction in said second transistor, and means coupled to said tube for introducing the potential of the collector electrodes of said first and said second transistors to said tube whereby said tube is blanked if either the vertical or horizontal sweep signals are absent.

11. In a television camera, a scanning tube for developing video signals, a D.C. biasing circuit coupled to the output of said tube for introducing a substantially constant current to delay the effect of a rapid change in the level of the light to said `scanning tube, a video amplifier capacitively coupled to said scanning tube. for receiving the developed video signals, means coupled to said tube for generating vertical and horizontal sweep signals and for introducing the generated signals to said tube for controlling the motion of the beam in said tube, and protection circuit means coupled to both said tube and said generating means for monitoring the generated signals and for blanking said tube when either the vertical or horizontal sweep signals are absent.

12. In a television camera, a scanning tube for developing video signals, a D.C. biasing circuit coupled to the output of said tube for introducing a substantially constant current to delay the effect of a rapid change in the level of the light to said scanning tube, and a video amplifier capacitively coupled to said scanning tube for receiving the developed video signals, said video amplifier including a transistor emitter-follower stage connected by said coupling means to said surface, a transistor amplifier stage coupled to the output of said emitter-follower stage, and a negative feedback loop coupled from the output of said amplifier stage to the input of said emitter-follower stage whereby the effective impedance presented by both stages is increased.

13. In a television camera, a pick-up tube for developing video signals, said pick-up tube having means for developing a beam of electrons and a light sensitive surface for receiving the beam, means coupled to said tube for generating vertical and horizontal sweep signals and for introducing the generated signals to said tube for con- 14 trolling the motion of the beam in said tube, and a pro. tection circuit coupled to both said tube and said generating means for monitoring the generated signals and `for blanking said tube if either the vertical or horizontal sweep signals are absent, said generating means including a vacuum tube multivibrator having a warm up time which is approximately the same as the warm up time of said pick-up tube whereby said pick-up tube remains blanked until the sweep signals are generated.

14. In a television camera, a pic '-up tube for developing video signals, said pick-up tube having means for developing a beam of electrons and a light sensitive surface for receiving the beam, a video amplifier, and means for capacitively coupling said amplifier to said surface, said video amplifier including a transistor emitter-follower stage connected by said coupling means to said surface, a transistor amplifier stage coupled to the output of said emitter-follower stage, and a negative feedback loop coupled from the output of said amplifier stage to the input of said emitter-follower stage whereby the effective impedance presented by both stages is increased, means coupled to said tube for generating vertical and horizontal sweep signals and for introducing the generated signals to said tube for controlling the motion of the beam in said tube, and protection circuit means coupled to both said tube and said generating means for monitoring the generated signals and for blanking said tube. if either the ver tical or horizontal sweep signals are absent, said generating means including a vacuum tube multivibrator having a warm up time which is approximately the same as the warm up time of said pick-up tube whereby said pick-up tube remains blanked until the sweep signals are generated.

References Cited in the file of this patent UNITED STATES PATENTS 2,141,343 Campbell Dec. 27, 1938 2,911,562 Fathauer Nov. 3, 1959 OTHER REFERENCES Publication No. l--Miniature ITV Camera Uses Drift Transistors, Flory et al., Electronics, Ian. 1, 1957, pp. 13S-142.

Publication No. 2-Television System for Stratoscope I, Flory et al., Electronics, June 17, 1960, pp. 49-53. 

1. IN A TELEVISION CAMERA, A PICK-UP TUBE FOR DEVELOPING VIDEO SIGNALS, SAID PICK-UP TUBE HAVING MEANS FOR DEVELOPING A BEAM OF ELECTRONS AND A LIGHT SENSITIVE SURFACE FOR RECEIVING THE BEAM, A D.C. BIASING ARRANGEMENT COUPLED TO SAID LIGHT SENSITIVE SURFACE AND INCLUDING A RESISTANCE OVER 100 MEGOHMS FOR LIMITING THE RATE OF CHANGE OF D.C. CURRENT FROM SAID SURFACE, A VIDEO AMPLIFIER, AND MEANS FOR CAPACITIVELY COUPLING SAID AMPLIFIER TO SAID SURFACE, SAID VIDEO AMPLIFIER INCLUDING A TRANSISTOR EMITTER-FOLLOWER STAGE CONNECTED BY SAID COUPLING MEANS TO SAID SURFACE, A TRANSISTOR AMPLIFIER STAGE COUPLED TO THE OUTPUT OF SAID EMITTER-FOLLOW STAGE, AND A NEGATIVE FEEDBACK LOOP COUPLED FROM THE OUTPUT OF SAID AMPLIFIER STAGE TO THE INPUT OF SAID EMITTER-FOLLOWER STAGE WHEREBY THE EFFECTIVE IMPEDANCE PRESENTED BY BOTH STAGES IS INCREASED. 